PINEHURST, N.C. (AP) — Martin Kaymer shot the best 36-hole score in U.S. Open history Friday with his second straight 5-under 65.

Taking advantage of a course softened by overnight rain, Kaymer was at 10-under 130 midway through a tournament he is turning into a rout. He matched the 36-hole mark at any major championship, set by Nick Faldo in the 1992 British Open at Muirfield.

Kaymer walked off Pinehurst No. 2 with a staggering eight-shot lead while many of the top contenders — including six-time runner-up Phil Mickelson and defending champion Justin Rose — were just teeing off.

The largest 36-hole lead at the U.S. Open is six shots, set by Tiger Woods in 2000 and matched by Rory McIlroy three years ago. Both captured the championship by large margins.

"It's not a done deal," Kaymer insisted. "You don't approach Saturday and Sunday in a relaxed way. There's never a time where you can relax. Unless it's Sunday afternoon and you're raising the trophy, then you can relax. Until then, you've got to keep playing."

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There were plenty of low scores to be had on the receptive greens, but no one went as low as Kaymer, who struggled through a swing change after winning the PGA Championship in 2010. He went through 29 tournaments and 18 months without a victory before winning at The Players Championship last month.

He's carried the momentum from Sawgrass to the sand hills of North Carolina.

"It's very, very satisfying," Kaymer said. "There were a couple of shots today; I was surprised at how good they were. I'm just hitting the ball very solid right now."

After closing the opening round with three birdies in his last five holes, Kaymer kept it going with his early morning tee time. Starting on the back side, he birdied the par-5 10th and pulled away from there with four more birdies. Even when his irons began to get away from him a bit, he made two nifty shots from the bunker at the sixth and seventh holes to save par.

Over the first two rounds, he's made 11 birdies and just one bogey.

"I struggled a little bit the last four or five holes, but I kept it fairly well together," Kaymer said. "I didn't make any major mistakes."

Brooks Koepka shot a 68 for a 2-under 138 total, leaving him tied for second with Dustin Johnson (69), Keegan Bradley (69) and Brendon de Jonge (70) of Zimbabwe among those in the clubhouse.

Top-ranked Adam Scott rebounded from a disappointing start to shoot 67. But Scott lost ground to Kaymer, winding up 10 shots behind with an even-par 140.

"It's great golf for Martin," Scott said. "When you're playing like that, you want to just keep it going. For him to come out today and back it up is super. If he does it for two more days, then we're all playing for second spot."